Xerographic camera



April 1953 w. E. BIXBY ET x. 2,831,409

XEROGRAPHIC CAMERA Filed July 18, 1955 EXHAUST PRESSURE SOURCE Fly. 2

United States vvXEROGRAPHIC CAMERA William E. Bixby and Robert S. Kriss,Columbus, Ohio,

assiguors, by mesne assignments, to The Helmet Company, Rochester, N. Y.a corporation of New York Application July 18, 1955, Serial No. 522,540

6 Claims. (31. 9s-- 1.7

This invention relates to .the field of xerography and particularly toan improved xerographic camera apparatus for the rapid processing ofxerographic plates.

.A process of electrophotography or Xerography is described and claimedin Carlson Patent 2,297,691, issued October 6, i942, and certain formsof xerographic apparatus for use in such a process are disclosed inCarlson Patent 2,357,809, issued September 12, 1944. Basically, theprocess of Xerography utilizes a Xerographic plate which in one form mayconsist of a metal plate or foil coated with a photoconductiveinsulating material such as sulphur, anthracene, an insulating form ofselenium, or the like. This coating is given a uniform electrostaticcharge onits surface, as by frictional rubbing with a cloth or brush,after which the plate may be exposed to a light image. The lightdischarges the coating in the areas which are struck by the light. Theremaining electrostatic latent image may then be developed with a finelydivided material, such as a powder or a liquid mist, to form a visibleimage. This visible image may then be transferred to paper or othersuitable surface and the plate may be cleaned and used again;

During the development of the art of Xerography, many advances andimprovements have been made in the various materials and methods thatconstitute the process to the point that Xerographic systems arecurrently in wide commercial use for the production of line copy andcontinuous tone copy, and adaptations of such systems for the productionof photographs by xerographic methods are in a highly advanced stage ofexperimental use. The most significant advances that have permitted thewide application of this art are improvements in the methods andapparatus required for charging and for developing the xerographicplates, as Well as improvements of the photographic response of thexerographic plates themselves, whereby xerographs may now be madeat'speeds and under conditions approaching these common in conventionalsilver photography.

For example, one advance which has been made in charging devicescomprises the substitution of a corona charging device, i. e., afilament connected to a high voltage source, for the frictional chargingmeans. Arrangements employing such a device are disclosed in CarlsonPatent 2,551,582, issued May 8, i951, in Carlson Patent 2,588,699,granted March 1952, and in copending application Serial No. 319,472,filed by C. R.

Mayo et at. on November 3, 1952. This arrangement permits the chargingof a plate to a higher potential than can be obtained frictionally andthe plate potential can bepredetermined approximately, by regulating thecharging voltage. and controlling the speed at which the plate is passedunder the charging source. Such an arrangement requires the regulationof the high voltage source and of the speed of the plate if closecontrol of the plate voltage, is. to be obtained so that it is ideallysuited for stationary equipment. in which power supply requirements canreadily be fulfilled.

A further innovation in plate charging apparatus is disclosed in CarlsonPatent 2,701,764, issued February 8,

1955, wherein a radioactive source is provided to generate 7 ions infront of a plate to be charged and an electrical eld is imposed to carrythe ionic charges to the surface of the plate. in an embodiment of thatinvention a radioactive source is supported in front of the plate and apotential source is connected to apply an electric field between thesource and the plate. By this arrangement the plate may be heldstationary during the charging cycle. With a device of this sort it isonly necessary for the operator to place the plate and the charging unitin juxtaposition for a period of a few or more seconds, depending uponthe size of the plate and the arrangement and type of radioactivematerial, in order to place a uniform electrostatic charge over theentire surface of the plate and condition it for use in making anexposure to a light image or other source of radiation to be recorded.

A further significant advance that has facilitated the production ofxerographic copy has been in the improvement of powder developmentmechanisms, for example, such as that disclosed in application SerialNo. 353,520. filed in the name of Eugene C. Ricker on May 7, 1953. In adevice of this sort a high pressure stream of gas is directed against apowder or carbon impregnated belt or ribbon and the powder particles areblown through a capillary tube whereby they are electostaticallycharged,

and are then blown through a chamber formed by the xerographic plate anda development electrode wherein the charged powder is attracted to theelectrostatic latent image on the plate and forms a powder imagecorresponding thereto. Using a device of this sort it isnow possibleto'develop a completeimage in a period of from one to three seconds.

A variety of improvements have also been made in the selection ofmaterials and methods of fabrication of Xerographic plates whereby thephotographic sensitivity and the spectral response of these plates hasbeen substantially improved; For example, the sulphur or anthracenefaced plates disclosed in Carlson Patent 2,297,691 have, in general,been replaced for commercial applications by selenium-surfacedaluminumbacked plates. Plates of this short are of such characteristicsthat they are ideally suited for use in the production of line copyalthough they are somewhat limited from the standpoint of photographicsensitivity and spectral response. Plates of this type are particularlyuseful for general commercial use because they may readily be charged toa uniform potential by any of a variety of types of charging devicesand, when so charged, retain the charge for appreciable periods of timewhen protected from exposure to light prior to the actual workingexposure.

The improvements in the field of Xerographic plate development have ledto a number of methods for producing highly sensitive, panchromaticXerographic plates capable of yielding good quality pictures. Ingeneral, these plates comprise a layer of vitreous and/or noncrystailineselenium in combination with one or more materials spread on a metallicbacking. Such plates have been found to have better than ten to fifteentimes the photographic speed of commercial selenium plates and areessentially panchromatic in their response to light. However, it isnoted that as photographic speed and panchromaticity are increased, thedark-decay rate of such plates also increases, 1'. e., even throughplates such as these are charged and handled under darkroom conditionsthe electrostatic charge placed thereon tends to decay in a very shortperiod when compared with conventional selenium plates. For example, insome instances it was found that in periods of from three to fifteenseconds after charging the plates had lot sufiicient of theirelectrostatic charge to make them unusuable for recording a xerographicimage. Such high dark-decay rates makes plates of this type impracticalfor use with usual darkroom procedure, inasmuch as too much time isrequired in handling the plate between the end of the char ing operationand the end of the development operation.

In usual darkroom procedure the plate is charged by passing it under acorona discharge and placing it in a plate holder. The plate is thencarried to and placed in a camera, exposed, and returned to the darkroomwhere it is removed from the plate holder. It is then placed on thedevelopment unit and the electrostatic image on the plate is developed.The shortest time in which this proceduce can be carried out in anyparctical commercial method is about one minute. However, in appreciablyless than one minute the potential on certain high sensitivityxerographic plates tends to drop too far, even in darkness, for theplate to be usable in making a picture.

In order to use such plates, the present invention discloses a rapidprocessing xerographic camera, whereby the plates can be manipulatedextremely rapidly in the interval between charging and development. In apreferred embodiment of the invention the camera comprises a hinge-typeconstruction wherein the camera back opens to permit placing the plateon a holder. When the back is closed the holder is positioned so thatthe plate is in the image plane of the camera lens. The plate is thencharged by means of a radioactive charging unit that is swung from thetop of the camera to a position directly in front of the plate. In thisposition, electrical contact is made and voltage is applied between theplate and the charging unit during the charging cycle. When charging iscomplete the charging unit is restored to its original position and theplate is exposed to the subject to be reproduced through a conventionallens mount ed at the forward end of the camera. Immediately afterexposure, the hinged plate holder is swung into operative relationshipwith the electrode of a powder cloud development unit. A charged carbonpowder is then blown into the development chamber formed by the plateand the development electrode whereby the electrostatic latent imageremaining on the plate is coated with charcoal particles. Whendevelopment is complete the plate may be removed from the camera totransfer the charcoal particle image by an conventional means, since thecharged charcoal particles when one in contact with the plate remainaffixed thereto by electrostatic attraction even though the originalcharge placed on the plate may decay entirely. By means of thearrangement thus proposed, the entire operation of exposure anddevelopment can be completed in a period of from two to three secondsafter the charging of the plate is completed.

The principal object of the present invention is to improve theconstruction of xerographic cameras for use with high speed xerographicplates. A further object is to provide improved apparatus for the rapidprocessing of xerographic plates. A further object is to provide acompact and convenient apparatus for charging, exposing, and developinghigh speed xerographic plates. Other objects of the invention will beapaprent from the following description.

A preferred form of the invention is shown in the appended drawings inwhich:

Fig. l is a cutaway isometric view of the xerographic camera of theinvention;

Fig. 2 is a functional schematic side elevation of the xerographiccamera of the invention in conjunction with a conventional powder clouddeveloping unit.

Fig. 3 is a schematic side elevation of the charging unit of the camerain operated position to charge a plate; and

Fig. 4 is a schematic sectional view of the development electrode,showing a xerographic plate in operative relationship therewith.

In the arrangement shown in Figs. 1 and 2 the rapidprocess xerographiccamera of the invention includes a light-tight, box-like structurehaving side walls 1 and 2,

4 top and bottom walls 3 and 4, respectively, and a front wall 5 inwhich is mounted any suitable and conventional lens and shutter element6. The rear wall 7 of the camera is conveniently hinged on bottom wall 4to provide ready access to the interior of the camera and may be latchedin closed position by any convenient means. Journaled in suitablebearings 8 in side walls 1 and 2 is a transverse shaft 9 that is mountedin a manner to have its axis of rotation parallel to the plane of thefocal plane of lens element 6. Fixed on shaft 9 are a pair of verticallyextending angle members 10 having rearwardly extending bars 11 thatserve to support a plate holder 12 that is provided with suitableinternal grooves on its side and bottom rails to support a xerographicplate 15 which includes a suitable metallic backing plate 14 having aphotoconductive surface layer 13. An upper rail 16 is provided to retainplate 15 in position in frame 12. The rearward ends of bars 11 abut theinner face of rear wall 7 when it is latched in closed position andserve to position plate holder 12 so that xerographic plate 15 is heldin the focal plane of lens element 6. A suitable detent device (notshown) may be provided to retain shaft 9 so that plate holder 12 ismaintained in a vertical position despite any movement of the camera. Avertically extending handle 17 is fixed to the outwardly extending endof shaft 9 whereby the shaft may be positioned as indicated in thedrawings for charging and exposing operations, or may be rotatedcounter-clockwise to facilitate the insertion andremoval of a plate, ormay be rotated in a clockwise direction through an angle ofapproximately 90 for developing operations, as described below.Preferably, plate holder 12 is formed of a suitable insulating materialto permit the application of a biasing voltage during the developingcycle, if desired.

In order to place a uniform electrostatic charge on xerographic plate 15the camera of the invention may include a radioactive charging unit 20which, for convenience, may be of the type disclosed in Figs. 2 to 4,inclusive, of the above-mentioned Carlson Patent 2,701,764. In a deviceof this type of radioactive source is provided to generate ions in frontof a plate to be charged and an electrical field is imposed to carry theionic charges to the surface of the plate. In the present unit thisdevice comprises an insulating plate 21 having affixed to its undersidea pair of narrow metal strips 22 which are electroplated with a layer ofpolonium 28, which in turn may be electroplated with a very thin coatingof gold which serves to protect the polonium but is sufiiciently thin topermit radioactive emission of alpha particles from the polonium intothe air. Plate 21 is supported by a pair of bar members 23 which in turnare fixed to a transverse shaft 24 that is journaled in bearings 25,mounted in side walls 1 and 2, for rotation about an axis that isparallel to the plane of the focal plane of lens element 6.

When the charging unit is inactive, plate 21 is held in a substantiallyhorizontal position by a suitable resilient detent 26 that is secured totop wall 3 of the camera. When the charging unit is to be renderedoperative for charging purposes, shaft 24 is rotated clockwise by ahandle 27 until the underside of plate 21 abuts the forwardly facingportions of angle members 10. This movement places the polonium platebars 22 in proper spaced relationship to xerographic plate 15 (see Fig.3) and, simultaneously, closes suitable electrical contacts (not shown)whereby, as fully disclosed in Carlson Patent 2,701,764, a D. C.potential source is connected between bars 22 and base plate 14 ofxerographic plate 15. The potential source has a voltage equal to orslightly greater than the potential desired on the charged xerographicplate. The operator maintains this relationship for the required time toelfect complete charging of photoconductive layer 13 on plate 15 andthen returns the charging unit to its substantially horizontal position.Plate 15 is then ready for use in making an exposure to a light image orother source of radiation to be recorded.

The following is belived to he an explanation of the process which takesplace during the charging operation just described: Alpha particlesemitted by the polonium layer into the air produce both positive andnegative gas ions (and electrons) in the space between bars 22 andbacking plate 14 of xerographic plate 15. If bars 22 are connected tothe positive terminal of the battery, the field is such .as to drivepositive ions toward the plate and negative ions and electrons in thedirection of bars 22. While many of the ions and electrons probablyrecombine to form neutral molecules before reaching either surface,there are many positive ions which reach photoconductive coating 13 onxerographic plate 15 and deposit their charge on it. As a positivecharge builds up on this photoconductive layer. the effective potentialof its surface is raised, thereby reducing the electrical field betweenbacking plate 14 and bars 22. Ions continue to deposit until a state ofequilibrium is reached as the potential of the charged photoconductivelayer on plate 15 becomes substantially equal to, or slightly less, thanthe potential of bars 22. in other words, the plate has then acquired apotential nearly equal to that of the D. C. source.

Although shown in conjunction with a radioactive charging unit it isapparent that the rapid process camera of the invention could readilyhave incorporated, as an alternate form of charging means, a stationarycorona charging unit of the type shown in copending application SerialNo. 495,945, filed in the name of James P. Ebert on March 2'2, i955.

After xerographic plate 15 is fully charged, charging unit 253 isrestored to its inactive position (as in Figs. 1 and 2) and xerographicplate 15 is exposed to a subject in a conventional manner by means oflens and shutter element 6. The apparatus is so arranged that a minimumof time passes between the end of the charging cycle and the actualexposure so that the plate potential will not decay to an unusableextent. As soon as the exposure is complete, handle 17 is rockedclock-wiseto engage Xerographic plate 15' with the development mechanismso that the development cycle may be initiated immediately, as describedbelow.

The development of the latent electrostatic image on the photoconductivelayer of xerographic plate 15 is accomplished in a development mechanismthat includes a development electrode 31 (see also Fig. 4) that ismounted in an insulating base member 32 which, in turn, is supported onbottom wall 4 of the camera. Electrode 31 is preferably of brass and isprovided with milled slots at either end one of Which, slot 33, servesas an inlet slot to receive charged powder particles from a powder cloudgenerator, and the other, slot 35, serves as an exhaust slot throughwhich excess powder particles and air are passed to an exhaust tube 3 6.Electrode 31 is surrounded by a resilient rubber gasket or O-ring 37which, when xerographic plate 15 is moved downwardly, is engaged by thesurface of plate 15 and thereby forms the side walls of a developingchamber, of which plate 15 forms the top and electrode 31 forms thebottom. Suitable shims 38 are mounted on electrode 31 and engage theouter edges of base plate 14 of the xerographic plate and serve tomaintain the proper spacing between the photoconductive layer on plate15 and the surface of electrode 31.

in order, to provide charged powder particles to develop the latentelectrostatic image on plate 15, the apparatus includes a powderparticle generator 40, of the type more fully disclosed inabove-mentioned application Serial No. 353,520, that is connected toinlet slot 33 of the development electrode by a capillary tube 34. Inthis arrangement a suitable pressure source 43, such as a pressure pumpor pressure reservoir which may, for example, be a container ofpressurized gas, is arranged to feed air or gas into a tube 44 connectedto powder cloud generator 40. Generator 40 comprises a suitable box orchamber 45 that is preferably sealed and relatively dust tight andcontains a powder impregnated tape or ribbon 46 that is fed from asupply reel 47 to a take-up reel 48 which may be rotated by any suitablemeans such as a manually operated handle 49.

In operation, pressure supply 43 maintains the powder cloud chamber at agreater than ambient pressure. The output of generator 40 is controlledby a suitable valve 50 controlled by a lever 51 which is actuated by aoperetc: when xerographic plate 15 is engaged with the developementassembly. When valve 50 is opened, a jet of pressurized air or gas isforced through nozzle 44 and blows a supply of powder particles fromtape 46 into capillary tube 34. Inasmuch as tube 34 is a capillary, thepowder particles in the air suspension will be in turbulent fiow and,through repeatedcontact with the walls of the tube, become chargedtriboelectrically to the proper polarity to be actuated to the latentelectrostatic image on the surface of photoconductive layer 13.

These particles enter the development chamber formed by plate 15,development electrode 31 and gasket 37, and are attracted to the latentelectrostatic image on the face of the plate. In usual operation,development of an entire electrostatic image is completed in a period ofapproximately one second by this type of apparatus.

In operation, the camera is loaded by releasing rear wall 7 andinserting a plate 15 in plate holder 12. To do this, shaft 17 is rockedcounterclockwise to move shaft 9 from its vertical detent position sothat plate 15 may more readily be inserted in plate holder 12. When theplate is inserted, handle 17 is returned to its vertical position andrear wall 7 is latched in closed position. The camera is then placed ina position in which the ultimate exposure is to be made. Immediatelybefore such an exposure, charging unit 20 is rotated into juxtapositionwith xerographic plate 15 and isheld there until the plate is fullycharged. This charging operation may require from five seconds to oneminute, depending upon the size of the plates involved and the size andrelative strength of the radioactive units that are employed. Whencharging is complete, unit 20 is swung to its horizontal position byhandle 27. and the exposure is made by means of lens and shutter element6. immediately after exposure, handle 17 is rocked clockwise to pressxerographic plate 15 into engagement with gasket 37 of the developmentmechanism whereby plate 15 is placed in proper relationship todevelopment electrode 31. As soon as this proper relationship isattained, the operator initiates a flow of charged powder particles intothe development chamber by means of lever 51 to elfect development ofthe electrostatic image.

With the type of equipment just described, the operations required fromthe end of the charging operation to the end of thedeveloping operationcan be completed in from two to three seconds. Thus, regardless of therate of dark-decay of the xerographic plate employed, the camera iscapable of effecting exposure and development of a xerographic imagewell within the usable period of plate potential.

Since many changes could be made in the above con struction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the drawings shall be interpreted as illus trative and notin a limiting sense.

What is claimed is:

l. A xerographic camera comprising a light tight boxlike structurehaving a lens element mounted in one Wall thereof, a shaft journaled insaid structure for rotation about an axis parallel to the focal planeor" the lens element, plate holding means arranged on said shaft tosupport a xerographic plate in the focal plane of the lens element, asecond shaft journaled in said structure for rotation about an axisparallel to the focal plane of the M r lens element, a xerographic platecharging unit fixed on said second shaft, a development'assemblysupported on a second wall of the box-like structure, means to rotatethe second shaft to move the charging unit into and out of chargingrelationship with a plate supported in the plate holding means, andmeans to rotate the first shaft to move the plate holding means to aposition to place a plate supported therein in operative relationship tothe development assembly.

2. A xerographic camera comprising a light tight boxlike structurehaving a lens element mounted in one wait thereof, hinged plate holdingmeans arranged to support a xerographic plate in the focal plane of thelens element, a xerographic plate supported by the plate holding means,a xerographic plate charging unit mounted for movement about an axisparallel to the focal plane of lens element, a development assemblymounted on second wall of the box-like structure, said developmentassembly including inlet and outlet ports for powder particles and agasket on the face thereof surrounding the effective area of thedevelopment assembly and said inlet and outlet ports, means to move thecharging unit into and out of charging relationship with saidxerographic plate, means to move the plate holding means to engage thexerographic plate with said gasket, whereby to form a developingchamber, and means for passing electrostatically charged powderparticles through said developing chamber.

3. A xerographic camera comprising a light tight boxlike structurehaving a lens element mounted in the front wall thereof, a shaftjournaled in the side Walls of said structure for rotation about an axisparallel to the focal plane of the lens element, plate holding meansfixed on said shaft to support a xerographic plate in the focal plane ofthe lens element, a second shaft journaled in the side walls of saidstructure for rotation about an axis parallel to the focal plane of thelens element, a xerographic plate charging unit fixed on said secondshaft, releasable detent means to retain the charging unit in anineffective position adjacent the top wall of the structure, adevelopment assembly supported on the bottom wall of the boxlikestructure, means to rotate the second shaft to move the charging unitinto charging relationship with a plate supported in the plate holdingmeans and to restore the charging unit to its inefiective position, andmeans to rotate the first shaft to move the plate holding means to aposition to place a plate supported therein in operative relationshipwith the development assembly.

4. A xerographic processing apparatus comprising a light tight box-likestructure having a lens element mounted in the front wall thereof, ashaft journaled in the side walls of said structure for rotation aboutan axis parallel to the focal plane of the lens element, plate holdingmeans fixed on said shaft to support a xerographic plate in the L focalplane of the lens element, a second shaft journaled in the side walls ofsaid structure for rotation about an axis parallel to the focal plane ofthe lens element, a xerographic plate charging unit fixed on said secondshaft, releasable detent means to retain the charging unit in anineffective position adjacent the top wall of the structure, adevelopment assembly supported on the bottom wall of the box-likestructure, means to rotate the sec- 0nd shaft to move the charging unitinto charging relationship with a plate supported in the plate holdingmeans to form an electrostatic charge thereon and to restore thecharging unit to its ineffective position, means to expose the plate toa light image to form an electrostatic latent image on said plate, andmeans to rotate the first shaft to move the plate holding means to aposition to place a plate supported therein in operative relationshipwith the development assembly.

5. A xerographic processing apparatus comprising a light tight box-likestructure having a lens element mounted in the front wall thereof, ashaft journaled in the side walls of said structure for rotation aboutan axis parallel to the focal plane of the lens element, plate holdingmeans fixed on said shaft to support a xerographic plate in the focalplane of the lens element, a second shaft journaled in the side walls ofsaid structure for rotation about an axis parallel to the focal plane ofthe lens element, a xerographic plate charging unit fixed on said secondshaft, releasable detent means to retain the charging unit in anineffective position adjacent the top wall of the structure, adevelopment assembly supported on the bottom wall of the box-likestructure, means to rotate the second shaft to move the charging unitinto charging relationship with a plate supported in the plate holdingmeans to form an electrostatic charge thereon and to restore thecharging unit to its ineffective position, means to expose the plate toa light image to form an electrostatic latent image on said plate, meansto rotate the first shaft to move the plate holding means to a positionto place a plate supported therein in operative relationship with thedevelopment assembly, and means for developing the electrostatic latentimage on said plate.

6. A xerographic charging, exposing and developing assembly comprising alight tight box-like structure having a lens element mounted in one wallthereof, hinged plate holding means arranged to support a xerographicplate in the focal plane of the lens element, a xerographic platesupported by the plate holding means, a xerographic plate charging unitmounted for movement about an axis parallel to the focal plane of thelens element, a development assembly mounted on a second wall of thebox-like structure, said development assembly including a developmentelectrode having inlet and outlet ports for powder particles and agasket on the face thereof surrounding the effective area of thedevelopment electrode and said inlet and outlet ports, means to move thecharging unit into and out of charging relationship with saidxerographic plate, means for exposing said plate to a light image toform an electrostatic latent image thereon, means to move the plateholding means to engage the plate with said gasket, whereby to form adeveloping chamber, and means for passing electrostatically chargedpowder particles through said developing chamber.

References Cited in the tile of this patent UNITED STATES PATENTS256,148 Lefeuvrier Apr. 11, 1882 2,588,675 Walkup et al Mar. 11, 19522,588,699 Carlson Mar. 11 ,1952 2,711,481 Phillips June 21, 1955 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,831,409April 2 1958 William Eo Bixby et ale It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Column; 2, line 42, for "short" read =--sort--; line 70,for "lot" read lest line '71, for umlsuahle read unusable-==-; column 3,lines 11 and 12, for "prooeduc'e" read -C-'proc'edure-'=-"; line 12, for"parctieal" read praetical g line 43, for "an" read -any line" 44, for"one" read -once' column 4, line 41, for fltype of" read --type e -3line 63, for "plate" read =-=-plated=-==; column 6, lines 11 and 12, for"developement" read dsvelopment---=a Signed and sealed this 8th day ofJuly 1958a (SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner ofPatents UNTTED STATES PATENT OFFICE ERTIHATE GE RRETEN Patent No2,83%409 April 22, 1958 William E0 Bixby et al0 Column 2, line 42, for"short" read ==sort-=--; line '70, for "lot" read. lost line '71, for"unusuable" read =-=-unusable-*= column 3, lines 11 and 12, for"proceducie" read procedure line 12 for "parctical" read. praeticalgline 43, for "*arp re'ad line- 44, for "one" read; oncecolumn 4, line41, for l'type of" read bype a -=3 line 63, for "plate" read===-plated==; column 6, lines 11 and 12, for "developement" read"'-=deve'lopment-== Signed and sealed this 8th day of July 1958,

(SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner ofPatents

